A) Field of the Invention
This invention relates to a communication management system and a communication management apparatus that constitutes a communication management system. More in detail, the present invention relates to a communication management system that transmits data to a network efficiently by managing states of a plurality of devices connected to a network and setting a master device to manage communication of all the devices connected to the above network.
B) Description of the Related Art
There is a standard such as the IEEE 1394 Standard and the like that transmits and receives audio digital data and the like via a network. According to the IEEE 1394 Standard, audio data and the like can be transmitted at a high speed, and also setting for a device connected to the network can be executed at a high speed. However, a standard of high-speed communication such as the IEEE 1394 Standard is for a short distance communication. For example, in a case that a high-speed communication is executed by the IEEE 1394 Standard, an actual transmission distance is 10 meters or less, and a long distance communication cannot be executed.
As a standard for transmitting and receiving audio digital data and the like via a long distance communication network, for example, there is a standard for transmitting and receiving a multi-channel uncompressed audio signal (audio digital data) such as the CobraNet (a trade mark) and setting information by Ethernet (a trade mark). In this standard, communication can be executed in a distance from 100 meters to a few kilometers. @
In a system that executes transmissions and receptions of audio digital data and the like via the long distance communication network, one of the devices in the system connected to the same network is set to be a master device (hereinafter simply called “master”) to manage a communication order, and other devices are set to be slave devices (hereinafter simply called “slave”). In this case, priorities of the all devices connected to the network are compared, and a device having the highest priority will be always the master device.
A device to be the master device transmits a transmission order of all the devices including its own device to the network, and other devices (slaves) transmits one by one in accordance with the order. When transmission of one device is finished, an instruction for starting the next transmission is transmitted to the next device, and a device having a next order (priority) receives the instruction and starts the next transmission. By repeating these processes, transmission of each device is made one by one at once.
In the device that executes transmission and receiving audio digital data and the like via the above long distance communication network, data is transmitted normally with a communication rate of about 90 Mbps. However, most parts (70 to 80 percent) of communication rate are used for communication of main data such as audio data, and setting information has lower priority than the main data. Therefore, the setting information and the like can use only a little part (one percent or less) of the communication rate, and communication speed is very slow.
In a case of confirming a state of other device (an external device) connected to a network is requested, it is necessary to obtain data representing the state of other device each time. At the time of confirming the state, a request for obtaining state confirming data is transmitted to the network, and it is necessary to wait for that other device transmits the state confirming data based on the request. Since the transmission speed of setting information is very slow, it requires a huge time. Therefore, it is very difficult to confirm quickly the state of other device connected to the network with the device described in the above.
Moreover, since transmission and reception of main data (audio data) are the highest priority with the device described in the above, other data cannot be transmitted and received during the transmission and reception of audio data. Therefore, the state of other device cannot be confirmed until the transmission and reception of audio data finishes.
Also, when other device (an external device) is newly connected to the network, priorities of all the devices connected to the network are compared each time, and a device having the highest priority will be a master. Therefore, a process to obtain the master is needed each time when a new device is connected.
Moreover, it is not preferable that a master is changed whenever a new device is connected, since process for obtaining a master is executed at a low communication rate, and it takes a great time.
Moreover, in the communication network described in the above, when data transmission of one device is finished, an instruction for starting transmission is transmitted to a next device, and the next device receives the instruction to start data transmission. During transmission of a certain device finishes and the next transmission is started any data do not flow on the network. Therefore, times when no data flows on the network likely to exist, and it will be difficult to transmit data efficiently.